Marine organisms, such as mussels, provide examples of strong adhesive systems that have not been mimicked well by human technology. Barnacles and marine mussels are able to affix themselves to virtually all types of surfaces, including metals, rocks and even polytetrafluoroethylene (PTFE, TEFLON™). They are capable of securing themselves over wide temperature range (−40 to 40° C.), fluctuating salinities, humidity and in the currents of marine environments. Mussel adhesive proteins have been isolated and sequenced. These proteins are rich in the unusual amino acid 3,4-dihydroxyphenylalanine (DOPA), which is believed to be critical for the formation of adhesive surface bonding and cohesive cross-links. The surface adhesion could originate from metal chelation, hydrogen bonding or radical-surface coupling provided by the catechol moiety in DOPA. Bulk cohesive strength has been found to be a result of oxidative cross-linking or metal chelation of DOPA. Various types of polymers carrying catechol groups have been prepared to investigate the nature of catechol functional group and to develop adhesives for specialty applications. Synthetic polymers incorporating DOPA-like chemistry have been explored with polypeptides, polyacrylates, poly(ethylene glycol)s, and polystyrene based systems. These materials, however, lacked the adhesion, elasticity, and/or degredation properties necessary for a soft tissue adhesive.
One intriguing application of these synthetic biomimetic materials is to provide the next generation of surgical adhesives and orthopedic cements. All surgical patients require a proper wound closure procedure to enable healing. Though devices such as sutures and staples have been used for many years, they are somewhat invasive and there are many potential sources of infection and inflammation of the wound area associated with these methods. Less invasive methods are continually explored in an effort to find optimal tissue adhesives. Cyanoacrylate based synthetic glues have been used as topical skin adhesives because they polymerize rapidly upon contact with water or blood. However, a limitation of these materials is moisture sensitivity and carcinogenic degradation byproducts. Another commercially available tissue adhesive is based on fibrin. Although this fibrin-based glue is made from human serum and is non-toxic, it is limited by poor mechanical strength. The ideal tissue adhesive design should incorporate simplicity, safety, efficacy, and possess setting times tailored for the specific clinical application. For commercial applications they should ideally be inexpensive, painless and cosmetic. Catechol-functionalized hydrogels have been developed as potential tissue adhesives and hemostatic materials. However, most of these adhesive materials lack tunability of elastic modulus and degradation rates for specific biomedical applications.
What is needed in the art is an inexpensive, painless and cosmetic adhesive design that incorporates simplicity, safety, and efficacy; mechanical strength; setting times tailored for specific clinical applications; and tunable elastic modulus and degradation rates for specific biomedical applications.